Plant Science Letters最新文献

A chloroplast phosphatase, distinct from fructose bisphosphatase, has been isolated and purified to apparent electrophoretic homogeneity from spinach leaves. This 100-kDa enzyme hydrolyzes both fructose and sedoheptulose bisphosphates. Given this lack of absolute substrate specificity, it cannot be considered a typical sedoheptulose bisphosphatase. The enzyme is reductively activated by reduced thioredoxin f_B in the presence of dithiothreitol (DTT), but not by thioredoxin f_A or thioredoxin m. Oxidized thioredoxin f_B deactivates the active reduced phosphatase.

The kinetics of inhibition by oligomycin of the mitochondrial ATPase and the Mg: ATP-dependent electrogenic transport of protons were compared in membrane preparations from radish seedlings.

Oligomycin blocks the phosphohydrolyzing activity of mitochondrial ATPase (measured at pH 8.5) at 1 μg × mg⁻¹ prot and the ATP-synthase one (measured at pH 6.6) at 3 μg × mg⁻¹ prot.

Oligomycin at these concentrations does not influence Mg: ATP-dependent proton transport and Mg: ATP-dependent hyperpolarization of transmembrane electric potential difference (PD) in microsomal vesicles. However, an inhibiting effect of the drug becomes apparent at concentrations higher than 10 μg × mg⁻¹ prot, increasing with the increase of oligomycin concentration at least up to 240 μg × mg⁻¹ prot. Both the vanadate and the NO₃⁻-sensitive systems of Mg: ATP-dependent electrogenic transport of protons show similar sensitivity to oligomycin.

Acetylene inactivates in vitro the reduced form of Chlorella NADH-nitrate reductase. In vivo acetylene atmosphere promotes the inactivation of nitrate reductase when the cell cultures were free of nitrate, more effectively under red light than under blue light. In vivo reactivation of acetylene inactivated nitrate reductase is nitrate and light dependent. The reactivation was also achieved in cells kept in media containing tungstate substituting for molybdate. For this in situ reactivation, blue light was much more effective than red light.

In vitro capitula (head-inflorescence) induction was observed in two varieties of Safflower (Carthamus tinctorius) from the inner surface of the cotyledons. Complete blooming of florets in a capitulum was observed within 55–90 days after inoculation. The pollen fertility of in vitro florets ranged from 90–95%. Embryo development was normal and a few seeds were also recovered.

Maize seeds imbibing at high temperatyres (above 37°C) germinate poorly, and their embryos show a low rate of protein-synthesis. Extracts of embryos imbibing at normal and high temperatures were able to translate exogenous mRNA, and poly (A) RNA obtained from them stimulated polypeptide synthesis by reticulocyte and maize cell-free extracts.

Embryos imbibing at 41°C incorporated insignificant amounts of [³H] adenine into poly (A) RNA and high M_r rRNA. Autoradiography showed that little transcription occurred in these embryos. Chromatin remained aggregated throughout imbibition at this temperature.

The results suggest that synthesis of new mRNA is essential for germination to proceed. Poor germination of maize at high temperature is probably due to the inhibition of transcription.

Lycopersicon glandulosum, L. peruvianum and L. esculentum plants reproduced adventitiously from cotyledon explants retained their resistance to the root-knot nematode, Meloidogyne incognita. This reaffirms the utility of tissue cultures for screening and isolating nematode-resistant variants.

Oxidized (inactive) chloroplastic NADP-malate dehydrogenase is 56-k Da homodimer, the two subunits of which are bound by a disulfide bridge. The enzyme is activated by three distinct chloroplast thioredoxins, thioredoxin m, f_A and f_B. When reduced by these proteins, the active enzyme is stable, whereas when reduced by dithiothreitol, activity is unstable. This result is apparently the consequence of aggregation of the reduced protein during prolonged incubation with dithiothreitol. At pH-values similar to those in the chloroplast stroma in the dark (pH 7), the reduced enzyme is still active.

The effect of initial pH of the culture medium (pH_i) on growth, changes in pH of culture medium (pH_c) and respiration of Dioscorea deltoidea cells was studied in cycle of batch cultivation. At pH_i 3.50 the lag phase of growth and respiration was about 24 h. Within the pH_i-range of 4.30–6.15 no lag phase was observed, growth and respiration being similar. At pH_i-values of 2.00–2.50 and 8.00 the cell population died. At pH 3.50–6.15 the level of pH_c was shifted to 4.6–4.7 by cells within 10–48 h. We suppose that the pH-regulation at pH_i range of 3.50–6.15 by the cells to a definite value of the pH_c (4.6–4.7) ensures their normal growthy cycle.

Growth and nicotine production were measured in callus tissue without organogenesis, derived from the petiole of Nicotiana tabacum L. cv. Burley 21 cultured on Murashige-Skoog medium (MS medium), T. Murashige and F. Skoog, Physiol. Plant., 15 (1962) 473, containing auxin α-naphthaleneacetic acid (NAA) and kinetin,at 25°C in the dark. Experiments clearly demonstrated that in the presence of a constant amount of kinetin, it is the auxin concentration in the culture medium that controls the rate of nicotine synthesis which follows a course almost parallel to callus growth. The maximum accumulation of nicotine in the callus (0.16% of dry wt.) is slightly higher than in the intact plant. A cytological examination of the callus tissue showed that the greater degree of cellular differentiation which causes the loss of meristematic areas, inhibits alkaloid synthesis.

In this paper we present the characterization of a differential morphogenetic response to cytokinin between two Petunia lines cultured in vitro. In particular, we report that: (1) two inbred cultivars of Petunia hybrida differed in the concentrations of cytokinin required to induce shoot morphogenesis from leaf explants and from stem epidermal explants in vitro. These differences were specific to the particular cytokinin utilized. (2) The F₁ hybrids of the two cultivars exhibited a biphasic morphogenetic response to cytokinin which was unlike that of either parent. (3) The cytokinin dose responses were similar in the reciprocal F₁ hybrids, indicating that the response is controlled primarily by Mendelian genes, rather than by cytoplasmic factors.